Conventionally, polymers that contain a high hydrogen bonding group with high hydrophilicity in their molecules, represented by polyvinyl alcohol (PVOH) and ethylene vinyl alcohol (EVOH) are used as gas barrier polymers. PVOH and EVOH are considered water-soluble polymers. Additions of up to around 20-30% ethanol or propanol to aqueous coating formulations containing PVOH and/or EVOH polymers are normal and provide longer cold storage stability and help increase the drying speed of these coatings formulations. It is also desirable to have an even higher content of lower alcohol or other organic solvents in such aqueous coating solutions in order to improve their stability and drying speed.
U.S. Pat. No. 7,157,147 B2 describes a gas barrier film comprising a thermoplastic resin film and gas barrier layer with a composition of a hydrolysate of a silicon dioxide, a polyvinyl alcohol base resin. A part of the polyvinyl alcohol was dissolved in a mixed solvent of 70 parts by weight water and 30 parts by weight ethanol.
CN 2010-1068086 discloses a barrier coating comprises a highly hydroxlyated polyvinyl alcohol. As part of the composition, the solvent is 1-25 parts by weight of the final composition. The solvent can either be methanol, ethanol, isopropanol, sec-butanol and/or isobutanol.
WO 2007034943 describes a coating comprising both PVOH and an ethylene-maleic anhydride copolymer being applied to a nylon film followed by heat treatment (at up to 220° C.). Based on the oxygen barrier reported, this organic-based coating would fall outside the terms defined by the parametric expression describing the ‘barrier improvement factor’.
JP 11-246729 describes compositions comprising PVOH, poly(acrylic acid) and clay and discloses how they are prepared under high pressure dispersion.
EP 1548074 describes a gas barrier coating material which comprises polyvinyl alcohol (A) and an ethylene/maleic acid copolymer (B) at an (A)/(B) weight ratio of 50/50 to 10/90 and contains at least one metal compound (D) selected from the group consisting of hydroxides, oxides, halides, carbonates, sulfates, nitrates, sulfites, and acetates of at least divalent metals selected from the group consisting of Mg, Ca, Al, Fe, Co, Ni, and Cu in an amount of 0.05 to 30% by equivalent based on the carboxyl contained in the copolymer (B); and a gas barrier laminate comprising a gas barrier layer made from the coating material and a plastic substrate wherein the gas barrier layer adheres to the plastic substrate either directly or via an undercoat.
EP 1666637 discloses a gas-barrier coating material capable of giving a packaging material which, when formed so as to have a thin gas-barrier layer. The gas-barrier coating material composition comprises as essential ingredients an ethylene/vinyl alcohol copolymer (A) obtained by saponifying an ethylene/vinyl acetate copolymer, a lamellar inorganic compound (B), and a solvent, wherein the sum of the ingredients (A) and (B) is 1 to 30 wt. % based on the composition and the proportion of (A)/(B) by weight is from 30/70 to 50/50.
JP2007136984 A describes EVOH-Clay composite coatings applied to a base layer having an anchor coat, prior to adhesive lamination to a second plastic film. The examples describe both polypropylene and polyester base webs, both requiring the use of an anchor coat prior to application of the EVOH-Clay composite. Although this reference notes a range of oxygen barrier of 1-7 in its claims there is no comment on the bond strengths achieved. Furthermore, this reference states that as the clay content increases, the adhesive lamination bond strength decreases.
WO2012168433 describes a packaging material made of cellulose, bearing a coating on the inner food contact surface based on an aqueous composition of poly vinyl alcohol and a cross linking agent optionally containing a platey or spherical shaped filler. The coating is said to provide barrier to hydrophobic compounds such as mineral oils typically found in recycled paper fibers used in the manufacture of recycled carton for food packaging.
WO 2013/017857 discloses a barrier composition for recycled paper based food packaging based on an alcohol based (PVOH is used to exemplify this) binder and an inorganic particulate. The barrier composition is claimed to prevent the migration of mineral oils, typically those found in recycled paper fibers used in recycled carton for food packaging.
WO2013066246A1 discloses a film or coating for preventing migration of substances from paper or board containing recycled fibers, wherein said film or coating is a polymeric film or coating comprising hemicellulose, wherein said film or coating is arranged to form a migration barrier layer.
In summary, none of the prior art described above discloses (gas) barrier coatings comprising poly vinyl alcohol and/or ethylene vinyl alcohol co-polymers dissolved in aqueous mixtures that contain at least 45% organic solvents such as lower alcohols.